In a network environment implementing a priority flow control system, if a first network device that is receiving lossless traffic from a second network device becomes congested with the lossless traffic, (e.g. if the queues assigned to the lossless traffic reach their capacity, or reach a threshold level), the first network device may send a message to the second network device indicating that the second network device should pause the transmission of the lossless traffic, (e.g. a “pause” message). In response to receiving the pause message, the second network device may enter a transmit off (XOFF) state for the queues assigned to the lossless traffic. In the transmit off state, the lossless traffic may be buffered at the second network device, rather than transmitted to the first network device. Once the lossless traffic congestion is cleared at the first network device, the first network device may send a message to the second network device that indicates that the second network device may resume the transmission of the lossless traffic, (e.g. a “resume” message). The second network device may then re-enter the transmit on (XON) state for the queues assigned to the lossless traffic, in which the transmission of the lossless traffic resumes. The priority flow control system may function seamlessly in a network environment that only includes a single VLAN (virtual local area network), and consequently a single spanning tree, since the single spanning tree may ensure that loops are avoided in the network.
However, a cloud computing system that includes multiple VLANs, and therefore multiple spanning trees, may encounter a deadlock state if each of the VLANs includes lossless traffic. For example, since each of the individual VLANs may include lossless traffic, it may be possible for the collective lossless traffic of the VLANs to form a loop that may become deadlocked. In other words, although the multiple spanning trees may ensure that loops are avoided for the traffic of the individual VLANs, in some instances the lossless traffic across all of the VLANs, in aggregate, may form a loop that may result in a deadlock.